I would not shoot unless I think he plans to shoot me or somebody else. Pointing a gun on the clerk's face is not enough.
Even though I think shooting the perp is perfectly justified, I honestly cannot make the shot under adrenaline, using a small CCW gun with small sight radius and less than perfect lighting conditions, that will hit the brain and immediately incapacitate him before he can apply a little more pressure on the trigger and kill the clerk.
The other issue is that the clerk and his employer have both decided on a policy that does not include resisting a hold up. He gives the perp the money, they write it off the taxes and move on. Do I have the right to change their policy on how to handle such serious events?
holy crap, whats it gonna take?